Thermoluminescent dosimetry, commonly referred to as TLD, is a technique for radiation dose measurement. Thermoluminescence is an emission of light which occurs when thermoluminescent (TL) phosphors are heated after having been exposed to beta, gamma, x-ray or neutron radiation. TLD has several known advantages over other dosimetry techniques such as film dosimetry.
TLD systems have been developed for monitoring personnel who work in the vicinity of radiation materials, X-ray equipment, etc. In such systems, each person being monitored is given a dosimeter to wear as a badge that consequently will be exposed to the same dosage of radiation as the person wearing the dosimeter. Although different types of dosimeters have been used, generally the dosimeters consist of an outer holder which houses a TLD card insert usually containing two, three or four TL elements in crystal form. The TLD cards and/or holders may be provided with a machine readable code to enable card and/or holder identification.
Periodically the TLD cards are processed through a TLD card reader to obtain an exposure record for each person being monitored. In the TLD card reader, the TL elements in each card are heated and the thermoluminescence is measured as by using a photomultiplier tube and associated electronic circuitry to provide a read-out of the TL integrals and/or glow curve. The data obtained by the TLD reader is then analyzed with the use of appropriate algorithms to obtain useful absorbed dose information. The design and response characteristics of the dosimeter coupled with the dose calculation algorithms which translate the dosimeter response to risk related quantity (dose equivalent) are among the most important factors which affect overall performance of a dosimetry system.
To control or modify the radiation admitted to certain TL elements in the TLD card, card holders heretofore have contained filtration media. Each TL element may be covered by its own unique filter which provides a different radiation absorption thickness to allow dose estimation for various organs in risk. The response of the thusly filtered TL element may be dependent on the angle of incidence. That is, the response of the TL element to a source of radiation at 0.degree. angle of incidence may be different from the response of the TL element to the same source of radiation at 45.degree. angle of incidence. Algorithmic correction schemes have been used to correct for angular dependence of delivered dose, but it would be desirable to minimize the angular dependence of the dosimeter where desired and when possible.